The archery sports of bowhunting and three-dimensional (3-D) archery requires range estimation. Unlike many forms of archery where the distance to the target is known, and where the archer and the target are in generally the same horizontal plane, bowhunting and 3-D archery involve targets placed at unknown distances and often involve steep uphill and downhill angles.
The ability of a 3-D archery or a bowhunter to determine the distance to his or her intended target, whether by range estimation or by using a rangefinder, is critical to shot accuracy. Unlike a bullet discharged from a firearm, an arrow's trajectory is very non-linear over relatively short distances. In the case of bowhunting or 3-D archery, incorrect compensation for target distance, together with the resulting arrow drop due to gravity, can lead to a missed shot, or worse, a wounded animal.
Several attempts have been made to provide rangefinding devices and methods to assist archers in estimating or determining target distance. However, for various reasons, the prior attempts to provide rangefinding devices and methods have proven largely unsuitable and inadequate for effective use in bowhunting and/or 3-D archery.
For example, one prior method of determining the distance to a target is by various bracketing techniques. One bracketing technique of rangefinding involves providing a transparent viewing window with movable brackets which allow the user to visually "frame" or bracket a target within the movable brackets. Once the target is bracketed, the distance to the target may be estimated by relating the bracket size to the target distance. A necessary assumption involved in this method is that the target size is always the same. As most bowhunters understand, however, the size of a given animal species varies considerably. Additionally limiting the usefulness of the bracketing method is the need for the user to adjust the movable brackets, either manually or electronically, during operation in attempting to bracket the target. Such manual manipulation of the adjustable brackets while preparing to shoot is highly time consuming and cumbersome. Often the shot opportunity lasts only a second or two. Finally, and perhaps most importantly, the bracketing method provides only a rough estimation as to the point-to-point distance from the user to the target rather than providing the more important horizontal distance between the user and the target. Simply put, bracketing techniques for rangefinding are imprecise, cumbersome, require too much time to carry out, and are based on assumptions that are inherently erroneous.
Another problem with respect to rangefinding relates to the uneven terrain involved in bowhunting and 3-D archery. On extreme slopes, either uphill or downhill, the distance at which the arrow must be shot to hit the target differs dramatically from the actual distance to the target. The reason is that an arrow generally will drop a given distance corresponding to the amount of time an arrow is in flight because of the constant force of gravity. Accordingly, the horizontal distance to the target is the primary factor that must be determined to accurately shoot on sloped terrain. Traditional prior art devices have not provided archers with a suitable solution for handling this problem.
Other known rangefinder devices employ the concept of triangulation, i.e., using trigonometric relationships to determine the distance to a target. For example, in U.S. Pat. No. 4,894,921, a triangulation device is described in which a weighted pendulum arm is attached to a rotary switch shaft. The pendulum rotates the switch as the bow inclination changes. The pendulum will actuate one of a plurality of switch closures, which in turn will cause one of several light emitting diodes or lamps to illuminate, indicating which sight pin should be used. While this device purports to compensate for various elevations by manually changing the pendulum's position relative to the switch shaft, this method of compensating for elevation would only be accurate if the trigonometric function relating elevation to distance were linear, which it is not.
U.S. Pat. No. 5,479,712 discloses another rangefinding device based on triangulation. This patent describes a device which utilizes a liquid crystal digital volt meter to numerically present the range without reading a scale. In this device, the distance to the target is determined by measuring an analog voltage signal which is proportional to the user's elevation and then is attenuated by a factor proportional to the tangent of the angle made between the archer's line of sight from the bow to the target and the line drawn vertically from the archer to the ground. The accuracy of this device is significantly limited by the inherent low sensitivity and low reliability of analog transducers. Specifically, since the signal in such a device must possess a specific characteristic, such as being proportional to a trigonometric ratio, transducers with high degrees of sensitivity and reliability cannot be effectively used. Accordingly, this device, at best, provides only an approximation as to the target distance.
Still another problem with respect to traditional rangefinding devices is that they do not provide any type of a movable sight which is automatically adjusted to correspond with a determined horizontal distance to a target. Rather, traditional archery bow sight pins are securely positioned at discrete increments such as for shots of 20, 25, 30, 35, and 40 yards, thus requiring the user to estimate the correct location between fixed sight pins for shots of distances other than those for which sight pins have been provided. Although single-pin, manually adjustable sights exist, such sights require the archer to physically adjust the pin to the proper location based upon the archer's perception of the proper distance to the target.
Lastly, and most significantly, a major limitation of traditional rangefinding devices is that they are not programmable. Indeed, none of the traditional rangefinding devices are capable of storing information for calibrating the device, or capable of other functions such as monitoring ambient conditions.
In view of the foregoing, there is a need to develop a rangefinding device which permits an archer to accurately determine the distance to a target. There is a further need to develop a movable sight which moves according to a determined distance to a target. Additionally, there is a need to develop a programmable rangefinding device. Still another need exists to provide a rangefinder device which may effectively utilize transducers with great sensitivity and high repeatability. A yet additional need exists to provide a rangefinder which calculates the horizontal component of the distance to a target to increase accuracy of bowhunters and/or 3-D archers when shooting on sloped surfaces.